Hi,
Ok so I have been able to manage the issue and have deleted your plugin through FTP, and have now access back to my site.
The FTP access problem had nothing to do with your plugin of course (I had recently attached an SSL certificate to the site, which implied to change the FTP settings to SFTP).
Unfortunately I wont be able to use your plugin unless you have a fix to the fatal error. If you have any alternative to recommend to use taxonomies on user please let me know.
Thanks